Sextant



' P. RINKEL Nov. 15, 1938;

SEXTANT Filed Aug. 17, 1936 Patented Nov.-15, 1938' UNITED STATES PATENT "orFicE Application August 17, 1936, Serial No. 96,506

' In Germany July 6, 1935 3 Claims. (Cl. 88-217) This intention consists of an improved sextant passes, after reflection by the two mirrors I and in Whiih jithe setting. can be particularly easily 9 and by the plane parallel prism members 8 and and reliably effected even from an unsteady posiinto the telescope, the image of the object obtion such as on'aircraft or ships. n served being shown sharply in the geometrical 5 The sextant in all 'its forms has an artificial plane bounded by the shutter l1. Another part 5 horizon device which consists, of a reflecting surof the parallel light reflected by the mirrors I0 face which adjusts itself independently of the and 9 strikes the-swinging mirror l2 and after manner in which the instrument is held. The reflection in the surfaces 1 and 6 also passes to mirror surface may be a level surface located the telescope. The image of the object observed,

10 externally of the instrument, for example, may reflected by the swinging mirror I2, is also shown 10 1 be a liquid mirror. It may, also, be connected sharply in the geometrical plane provided by the with the instrument either as a liquid mirror or shutter l1. As the one image is reflected by an a mirror (swinging mirror) rigid in itself and even numberand the other by an uneven number floating and/or rotatable in bearings (suspended of mirror surfaces, the one image is' seen upside mirror) which may also be inclined in relation down and the other in erect position. 15

to the horizon. In Fig. 2 is shown how the field of vision bound- Various embodiments of the invention are ed by the shutter l1 appears.

illustrated by way of example in the accompany- The po nts 0 Shown in full lines, indicate ing drawing. three star images visible in the field of vision. -m' In the drawing: The three small circles a, b, 0' denote the re- 30 in Fig. '7.

Fig. 1 is a diagrammatic view in side elevation flected images of the same three stars. The and partly in section illustrating one arrangedotted line is the line of symmetry of the two ment of the optical elements of the sextant. superp e im O h line appe r h image Figs. 2, 3. 4 and 5 illustrate the field of vision and the reflected images of all those points of bounded by the shutter of Fig. 1. the firmament for the altitude of which the 25 Figs; 6 and 7 diagrammatically illustrate ansextant is set. 1 other form of the sextant wherein Fig. 7 is a In order to obtain better observation of the side elevational view partly in section and Fig. 6 lation of the ima e and the reflect d im e is a cross-sectional view of the elements shown one of the two images may be oifset slightly in relation to the other. The image then appearing Fig. 8 is a diagrammatic elevational view of a in the field of vision is shown in Fig. 3. Three scale arrangement 'for the sextant. star images d, e, ,f are visible. (1, e, f denote In the embodiment illustratedin Fig. 1, I dethe laterally displaced reflected star images. The"-- notes a telescope with the objective 2; the eye sextant is set for the star f. 1 i

' piece 3 and the eye lens 4. In front of the objec- With the sun an d moon, as soon as the'image tlve 2 is located a pentagonal prism 5 with the and the reflected image come into register, & reflecting surfaces 6 and 1. The prism 5 for the bearing of the centre of the sun or the moon is passage of the rays extending therethrough is provided. If only the upper or lower edge is 3? extended by means of a prism wedge 8 to a body visible then the upper or lower edge itself can 40 with parallel planes. at once be observed as shown in Fig. 4. 40 The reflecting surface 6 is transparently mir- Moreover, provision may be made for sub-divirored while the surface 1 is entirely mirrored. sion of the one and preferab y the ima e 110 9 is a fixed mirror; 'I 0 a mirror rotatable about efle d n o tWo i a e o e above the other.

the axis as in the known arrangement of ordinary his esu t can be attained by means of a double mirror sextants. The angle between the fixed prism or by means of a Wollaston prism l8, which 45 mirror 9 and the rotatable mirror l0 alone deteris interp e if desired n front o the p a o al mines the altitude of the star observed. prism in the path of the rays (shown in dotted I2 is a mirror arranged beneath the pentagonal lines in Fig. 1) I v prism 5. The mirror I2 is secured to the swinging This procedure is convenient when the position member l3. I4 is the axis of the swinging sysof the observer isparticularly unsteady and the tem I2, l3. The member 13 serves in the example star image observed is continuously oscillating or shown both as a damping disc which swings bevibrating. In taking a bearing of the star the tween the poles of a braking magnet l6. Other unsteady reflected moving image is permitted to damping devices may, however, also be used. swing between the steady double image. In Fig. 5 The parallel light from the object observed 5 the zig-zaglines g, h, 1" denote the vibrating image, 99, Mt, ii the double images of the corresponding three stars.

The angle of deflection of the pentagonal prism I is in the example shown 90, the angle of inclination of the swinging mirror 45. when this angle of inclination diflers from 45 it makes no difference. The instrument should then be used in a position differing from the horizontal by the same amount in order that the line of symmetry of the image and of the reflected image comes in the centre of the field of vision.

In order to give the new sextant a stumpy form in particular in order to be able to keep the mirrors 3 and II small, it is preferable to arrange the paths of light for the image and the image to be reflected not in a position one above the other as shown in Fig. 1 but side by side.

In Figs. 6 and 7 is shown how this result can the attained.

no In front of the objective 22 of a telescope 2! is located the mirror 23 pivoting about the axis 23. Beneath the latter is arranged the pentagonal prism 24 with the reflecting surfaces 25, 25'. In front of the prism 24 is disposed a Fresnel prism 25 with the reflecting surfaces 21 and 28. This prism 25 is arranged at an inclination in such manner that the path of the light is displaced parallel so far upwards and laterally that it lies at the same height as the path of light for the non-reflected image. The arrangement is shown in Fig. 6 in cross section.

- the fixed mirror and the mirror rotatable about the axis 3i in a known manner.

It is particularly simple to arrange the new sextant so that it can be used for taking observations with a natural horizon. In the embodiment shown in Fig. 6 the two'mirrors 29 and 30 are extended for this purpose to the one side. Parallel to and adjacent the telescope 2! is located a second telescope 32. On observation through this telescope 32 the stars are observed by way of the fixed mirror 29 and of the rotatable mirror 33 and adjacent the fixed mirror 29 the natural horizon is observed. The arrangement consisting of the swinging mirror and the prism thus do not lie in the path of the rays.

In Fig. 8 is shown diagrammatically a special scale arrangement which cannot be fitted to known sextants having a swinging arc.

The index arm 34 with the index 35 is firmly connected with the rotatable mirror 33. With the rotatable system 33, 34, 35 is connected 9. scale carrier 33 which has a scale 31 and a pointer 33. The pointer 33, on rotation of the system 33 to 33, passes along the arc 39 on the scale carrier 43. If now the index 35 is adjusted to the zero point of the scale 31 located in the middle and the system 33 to 38 is turned as a unit about the common axis, then by means of the pointer 33 the set altitude can be read off on the scale 33. If a definite expected value is set on the scale 33 and fixed in this position and then on the observation only the arm 34 with the mirror 33 and the index 35 is moved then by means of the pointer 35 the difference between the actual and expected angle can be read off on the scale 31.

The further necessary and usual devices such as dark shades, a protecting casing for the swinging devices, vibration devices for reducing the approximately horizontal direction.

As the heavy segment on a pendulum is dispensed with very much shortened periods of vibration can be obtained.

It is particularly suitable to form the damping disc serving as a pendulum weight as a pendulum having the minimum period of vibration.

The arrangement for observing the natural horizon permits control of the artificial swinging mirror horizon and inversely there can be determined whether an unreliable natural horizon can be used for a measurement. Finally the dip of the horizon can be measured by reflection of the horizon on itself.

Having described the nature of the invention and the manner in which the same is to be performed, I claim:

1. In a sextant, an index mirror for reflecting light proceeding from an object to be observed, an eye-piece arranged at one end of the sextant, a fixed mirror positioned at the other end of the sextant for reflecting the light of the index mirror in a direct path into the eye-piece so that a first image of the object may be viewed at the first end of the sextant, angularly disposed transparent reflecting means interposed in the direct path of the light reflected by the fixed mirror allowing the light forming the first image to pass therethrough, reflecting means arranged intermediate the fixed mirror and the eye-piece and positioned laterally of the direct path between the fixed mirror and the eye-piece including at least two angularly arranged complete reflecting means one for intercepting light forming a. second image of the observed object proceeding from the fixed mirror and the second complete reflecting means reflecting the light forming the second image transversely with respect to the direct path of the first image onto the transparent reflecting means, said transparent reflecting means being arranged to reflect said transverse light image into said eye-piece, and one of the reflecting means intermediate of the fixed mirror and the eye-piece being swingably mounted to be moved by gravity.

2. In a sextant, an index mirror for reflecting light proceeding froman object to be observed, an eye-piece arranged at one end of the sextant, a fixed mirror positioned at the other end of the sextant for reflecting the light of the index mirror in a direct path into the eye-piece so that a first image of the object may be viewed at the first end of the sextant, a pentagonal prism interposed in the direct path of light reflected by the fixed mirror, one face of said prism having a transpar- I ent mirrored surface permitting the light forming the first image to pass therethrough, another face; of the prism having a completely mirrored sur- 2,136,995 'face so as to reflect a transverse beam of light onto the transparent mirrored surface 01 the prism, said transparent mirrored surface being positioned to reflect the reflected transverse beam of light into the eye-piece, and a pendulum actuated mirror positioned laterally of the direct path of light forming the first image and arranged intermediate of the fixed mirror and the eye-piece for reflecting light forming a second image proceeding from the fixed mirror onto the completely mirrored surface of the prism whereby the second image is inverted in being reflected into the eyepiece. n

3. In a sextant, an index mirror for reflecting light proceeding from an object to be observed, an

eye-piece arranged at one fixed mirror positioned at sextant for reflecting the mirror in a direct path into end of the sextant, a the other end of the light of the index the eye-piece so that a first image of the object may be viewed at the first end of the sextant, a transparent swingable mirror interposed in the direct path of light forming the first image and adapted to be moved by gravity to reflect transverse beams of light into the eye-piece, a pentagonal prism arranged laterally of the direct path of light forming the first image, said prism having two mirrored surfaces and one mirrored surface being arranged to refleet light onto said transparent mirror, and prism reflecting means positioned intermediate the fixed mirror and the pentagonal prism for intercepting light from the fixed mirror and reflecting the same onto the other mirrored surface of said pentagonal prism to provide a second image of the observed object which appears inverted in the I eye-piece in being reflected thereinto.

PAUL RINKEL. 

